Fly wings, and other things of a bunch.

[Vhaerun]

With that in mind, I'd say to allow skill casting consumables over not allowing them. If it could be tailored with a variable or something to allow wings to be used while casting but disallow other skill casting items that would act as a cast cancel(if that is how it would react), that'd be even better.

Still though, if that can't be done, it would be balanced out a bit by said consumables being uncommon and not sold by npcs.